Amplifier system



Apr 2, 1932- s. Y. WHITE 1, 3,

AMPLIFIER SYSTEM Filed Aug. 17, 1928 INVENTOR.

ATTORNEY PatentediApnflg; 1 932;

; Lassusr snnmif Y. warm- (or; NEW 'YOBK,

ASSIGHOB'; BY E. ass emtmshro RADIO" CORFORAt LION OF AMERICA, OF NEW YORKy N. Y i,*A'. "GOB PORKTION E DELAWABEI am utation filed August 1?, 192a. suntan. 5

The presentinvention relates generally to amplifier systemsandEparticularly to such systems employing three-electrode vacuum continuation in part of .my-

tubes. It is a b co-pendin application Serial Number 207,- 607,filed uly 22, 19271.1;

An object of the invention is tofix the action of amplifier s stems from frequency to frequency over wi eranges of frequency in those systems employing variable selective circuits tocover wide ranges of frequency,

and particularly where such circuits are used.

with three-electrode vacuum tubes having inherent. internal capacity introducin conpling effects between tube output an in ut circuits which are not constant with requency.

One object is to maintain overall amplification constant from frequency to frequency over a wide range of frequencies, or to control the amplification in a desired way with frequency variation produced by means of selective circuits.

Another object is to controllably off-set;

from frequency to frequency over a wide range of frequencies the reactive effects through the internal capacity of three-electrode vacuum tubes.

A further object is .to maintain manually operated elements of tuning devices of the system at low or ground potential to avoid well known body capacity efi'ects particularly apparent in connection with high frequency systems, and especially so when regeneration in three-electrode vacuum tube operation is present.

Other objects and the advantages thereof .will be readily recognized by those skilled in the art from the description to follow with the aid of the figures of the accompanying drawings;

Fig. 1 diagrammatically tem of circuits associated illustrates a syswith a three-electrode vacuum tube to embody the features of the present invention.

Fig. 2 diagrammatically illustrates employment of features of the invention in the radio frequency portion of a radio receiver.

Like reference characters represent like parts so far as possible in the two figures. I

sys'rm Referring first to Fig; 1, a threeelectrodei vacuum tube isshown to have a: tunable c1rcu1t,includin'nductance coil L hand tun: mg condenser Hz connected across its 'igridl. andfilament electrodes, and there. m cnotb l e a gri ic ns Ci. leak resistance R depending upon,- e fu ell tion for which he tube is mployment use or non-use of'these elements under different conditions of coperation bein I ivell sues-a: stood in the. art. v'llheplat andfilamen lee l trodes are shown connected through s'afi ndii cated. impedance 1, which maybe. anytime; impedances encountered l in I. connectin vacuum tubes for 1 operation. many {one} of the numerous purposes and modeslof em ployment ofthem now common to practice. For :example, theimpe dance I maybe the capacitive to high frequency current imped ance of an audio frequency transformer in the .case of the tube fbeingused as a detector. of modulated h fre uenc currents, asis the case of tube T in'l'Fig. 2; or the capaci tive tohigh frequency current impedance had when a hoke coil or resistance, is used asth'e; interstage ,couplinginabroad band high fre-. quency amplifier; or; again the variableima pedance had when a tunable circuit or coupled tunable circuit is used fasthe interstage' cou-, pling, as is the case betweentubes VT and. 80 VTinFig.2. f f

The energizing of the electrodes of the tubes is conventlonally illustrated in both figures, and is too well understood to require detailed reference.

The inherent internalcapacity of the tube may ' between filament and plate electrodes ism-.-

H mea 5; that the phase of the reflection depends upon. the nature of-theeimpedance, being 90" out f the ei t h use, imrsdnwfie 1 0 1-- reactiye .andthus, neutral\ or non-.eifectiveon;

e c genrgy flesist esi hase histhenetmsnns when the plate impedance is inductive, thus roducing increased or nerative amphcation even to self-oscillation; and opposing phase when the plate impedance is capacitive, thus decreasing amplification.

If the s em is planned to cover a w de of uencies, as by making tuning ndenser C, widely variable, it is apparent that the efiect of internal capacity varies from f uency to frequency throughout the at 13, the capacity remains subatantially constant irrespective of frequency, and is a more effective coupling at high frequen than at low frequency. Again the impe ance of any particular device used in or in association with the plate circuit can be expected to difier considerably from frequency to frequency over a wide range of frequency, so that the reaction thereof which forces energy through the internal capacity C. is not constant with frequency. For example,iftheim ceIinFig. listhe capacitively. reacting impedance of an audio frequenc transformer such as T in Fig. 2, its capacitive reaction to high frequency currents will be less at higher freq at lower frequenc thus bringing a ut a difference in feedack through internal capacity C, from frequency to'frequency. If the im dance I is a variable one, as is the casea tumble inter-stage eeuplin such as that shown between tubes VT and in mi eudri wmable'lrrmgement may not be constant with frequency. For example, if the tunable circuit is coupled to the plate circuit, as is the case of the arrangement in Fig. 2, the degree of coupling may change substantially from frequency to frequency. Also the necessity for varying the tuning condenser C, of Fig. 2 to have this circuit follow the tuning of the input cir- 'cuit of tube VT will change widely the ratio of inductance to capacity, which change in ratio will substantially affect the impedance.

It is thus apparent that this coupling between grid and plate circuits introduced by the filament-to-plate capacity of three electrode vacuum tubes, which permits of influencing the amplifying ability of the system enormously in the high frequency regions, together with the lack of constancy with frequency of-the reactions vof physically constructed electrical elements which must be used to make'niliF circuits, makes the matter of securing'u orm performance, or predetermined performance, with frequency a difficult one. Often such control over the rformance with frequency is highly desira 1e, as for example in the case of a broadcast radio receiver which preferably should ive the same performance from the neigh rhood of 500 kilocycles to 1500 kilocycles, a ve wide range of frequency.

in, it is often desirable to change the uenc than sign to overcome these difliculties in phase character of the reflection from the plate circuit back on to the grid circuit through the internal capacity of the tube from that obtained by reason of the employment of elements to perform certain required functions. For example, if the impedance I is that of, an audio frequency transformer in the plate circuit of a vacuum tube used as a detector, which transformer is needed to filter the signal representing modulations from the rectified highfrequency current, the inherent capacitive reactance to the high frequency currents pic-laces a feed back through internal capacity C, out of phase with the high frequency energy in the tuned grid circult, which out-of-phase feed back reduces substantially the amplifying ability of the system, and also has the effect. of apparently increasing the damping of the tuning in the grid circuit to lessen selectivity. In the case of the tunable inter-stage coupling the attempt to maintain the tunable coupling circuit in resonance with the tunable Input circuit inevitably results in producing an inductive reaction in the plate circuit which feeds back to the gridcircuit in phase with the high frequency energy thereln, thereby materiall increasing the amplifying ability of the tu and so much so that if the coupling is tight oscillation will be produced on tuning the coupling circuit with res ect to the tuned input circuit, an undesire effect nhyihe .inJ-henae .ofan intended amplifying sys- "tem. Fultherpifthe effective impedance of the turnable coupling circuit back onto the plate circuit varies from frequency to freuency, as is generally the case, it may be that t e reactive potential is suflicient to produce oscillation at one end of the frequency band and is not flficient to produce oscillation at the other end of the band, thus reducing the width of the band for which the arrangement is satisfac y operative.

These dificulties can be and have been overcome by including in systems of the kind under discussion manually variable electrical elements, which can be adjusted from frequency to frequency to overcome the difiiculhas as they arise. Such arrangements are more successful in the hands of skilled operators, and are undesirable and not wanted in the more popular uses of radio and like devices now being distributed for entertainment purposes.

The present invention is directed to the end of provi an arrangement in which electrical elements can be predetermined in dermanently fixed form, and thus avoid fo ow-up adjustments from point to point in a system covering a wide range of frequencies. To accomplish the result I employ an auxiliary coupling between the grid and plate circuits to oppose the efiects produced by the coupling between these circuits arising from the inherent internal capacity of the three-electrode tubepand arrange the auxiliary coupling so that it can be predetermined to feedack in any desired way with frequency to 5 follow the feed-backthrough the tube inherent to the use of certain elements for detroma etic coupling is correct to phase.

with t e electrostatic coupling. In my copending application 48,936 of August 8, 1925, I ave set forth in detail how the ener transfer of an electromagnetic coupling ecreases with decrease of re uency and how the energy transfer of an e ectrostatic coupling of the kind shown increases with decrease of frequency, and how the two transfers can be combined to produce an over-all transfer remaining substantially constant with frequency, or varying in any predetermined way with fre uency, by proper selection of the relative egrees of the two coupling effects, and have particularly pointed out how I princi ally control the resultant effect by choice 0 the czpacit relations between tuning condenser 2 an coupling condenser C It is therefore obvious that with this combination of coupling I can predetermine an auxiliary feed back from the plate circuit to the grid circuit that will oppose in any desired way the feed back due to internal capacity C acting in accordance with the impedance I of the particular element used in the plate circuit of the system, and can thus make the action of a system such as that shown in Fig. 1 substantially constant with frequency over a very wide range of frequencies, or vary in any predetermined way with frequency from-the inherent way of action imposed by internal capacity C and the nature of impedance 1.

The connection as shown opposes the feed back through the tube no matter what may be the nature of the reactance of the impedance element I, this because the combined electroma netic and electrostatic coupling reverses the phase of the reaction passing through condenser C Thus, if the reaction in the late'circuit is capacitive to produce a deamp ifying feed back through C the feed back through the auxiliary circuit and its combined coupling produces a regenerative effect 'to lessen tie-amplification any desired. (3 amount, or reverses it to produce regenerative amplification, and may be even adjusted strong enough to produce oscillation, this either by adj ustin the value of condenser (J, or the-degree of e ectromagnetic and electrostatic couplings.

There is shown in dotted'lines'a source S of alternating current coupled to the input of the system through coil L,, which source may be one of high frequenc modulated currents to be either amplifie 1y repeated and passed on to a subsequent a stem by means of proper choice of element or impedance 1, or amplifiedly detected for transfer to a responsive device or audio amplifier. Or'the source S may be one of continuous or unmodulated currents, inwhich case theauxiliary. circuit may be adjusted to ive enough feed back to produce oscillation or so-called selfheterodyne reception of the continuous waves, and in this case it is ossible to so adjust the auxiliary circuit an its coupling that the system may be maintained slightly 1n oscillation throughout the entire range of tuning covered by condenser G which effect has heretofore not been possible with the feedback coupling arrangements between grid and plate circuits of systems used in connection with so-called self-heterodyne reception. Or the system may be used simply as an oscillation generator for producing high frequency oscillations for any purpose, but with which it is desired to be certain of producing substantiall the. same magnitude of oscillation throng out a wide range of frequencies merely by varying the tuning condenser C In this case the source S would be eliminated, and an'element for impedance I chosen to pass the high frequency oscillations out of the system to any desired point of use. It will be further noted that in the arrangement shown the coupling condenser C and the tuning condenser C are so related that the tuning condenser C is directly connected to the filament system of the tube, the oint of lowest high frequency potential of tie system, and may be thus connected to aground G as is common in vacuum tube amplifier systems. Assuming that the condenser C 18 of the usual stator-rotor type, the rotor side can be the grounded side, thus eliminating body effects by reason of the operator having to handle the rotating arrangement. This form of connection varies thedifference of potential across condenser G with frequency, and therefore the difference of potential across the grid and filament of the tube, as the ratio of the capacity of condenser C to the capacity of condenser C is varied by altering the capacity of condenser C for tuning. In general practice the capacity of coupling condenser C is large compared to the capacity of tuning condenser C- so that the ratio will not be changed to such a degree that the flexibility of the combined electromagnetic and electrostatic coupling static couplingl is of particular value in connection with t e so-called single dial control of a multiplicity of stages of radio frequenc amplification, where it is desirable that al of the rotors of the several stages connected 1. throu h a single control element be at one and t e same potential and the lowest potential.

In Fi 2 the features of the invention are shown a apted to a radio receiver as follows:

Tube VT is connected and energized for do tection of high frequency modulated currents am lified in tube VT and transferred to tube V by way of a tunable coupling circuit including inductance L and tuning condenser (7 In this case the impedance of audio frequency transformer T in the output circuit of the detector reacts capacitively to the entire high frequency band which tunable circuit L C covers, thus causing the system to de-amplify for all frequencies while detecting. The capacitive reactance of transformer T is indicated by the condenser C, in dotted lines. The de-amplifying feed-back through the tube is opposed by an auxiliary circuit coupling the plate circuit and the grid circuit by way of condenser C, and the combination of electromagnetic coupling between coil L and L and electrostatic coupling afforded by condenser C as described in connection with Fig. 1. The feed-back by means of the auxiliary coupling can be made of any degree desirable, so that the detector tube may be made neutral in the matter of over-all feed-back, or may be made to regeneratively amplify to any desired degree by adjustments described in connection with Fig. 1, and the effect made constant with frequency or varying with frequency in a predetermined way as before described.

Tube VT is connected and energized to amplify at high frequency, the high frequency modulated currents being impressed upon the tunable input circuit L- C 1 through an antenna W connected to ground G by way of inductance L 1 and condenser (3' thus giving a combined electromagnetic and electrostatic coupling between the antenna and the tunable input circuit. A low capacity high frequency choke coil K, shunted around coupling condenser (1",, provides for a direct current bias to the grid of tube VT. The output circuit of tube VT is coupled electromagnetically and electrostatically to the detector tunable circuit L,, C, through the inductive couplin between coil L and coil L, and coupling con enser C This tunable inter-stage coupling may be responsible for a variable with frequency impedance in the plate circuit of tube VT, and if the coupling ls'tight enough there will inevitably result suficient inductive reaction as tunable circuit L C, is adjusted to produce oscillation by reason of feed back through inherent tube ca- Eacity C., unless the effect is opposed to sufcient degree. The necessa opposition is provided or by means of auxiliary feed back circuit L and C;, which can be adjusted as before described to give any amount of auxilia feed back needed and to act in any desire way with frequency.

It will be noted that in case of Fig. 2 the combined coupling in the case of both tubes is made to serve the double function of transferring energy forward and transferring energy backward from plate to grid circuit. It is not difiicult to bring this double function into satisfactory operation, because the combined coupling may be primarily designed to give the right amount of energy transfer forward, and the feed back effect then satisfactorily controlled through selection of the values of feed back condensers C and (3,. However, the energy transfer coupling can be made independent of the feed back coupling as indicated in Fig. 1. I

The flexibility of the combined electromagnetic and electrostatic coupling permits of adjustment to arrive at an opposing ener that will take care of the resultant tube fee back energy of a combination of effects inherently different from fre uency to frequency, whereby a substantially over-all uniform amplification eifect for the system, or variation from this uniform effect if wanted, is possible.

It will be noted that tuning condensers C, and C, each have one element at a common or ground potential, so that the arrangement provides for connecting the rotors of these conductors to the same shaft for single dial control without introducing difference of potential difliculties.

The high frequency, low capacity choke coil K permits of energizing the plate electrode of late VT around coupling condenser C wit out materially affecting the coupling conditions. The electrodes of the tube are indicated in a conventional manner as suitably energized for the intended purposes of operation.

The invention is one capable of numerous applications in the various practices of the art which will be readily apparent to those skilled in the art, and no limitations are intended by reason of the selection of the particular systems embodied in the drawings for descriptive purposes.

Having thus described my invention, I

claim:

1. The combination of a three-electrode vacuum tube, an input circuit, an output circuit, a tunable circuit in one of said circuits, an impedance element in the other of said circuits, and a connection from a potential point created by said impedance element, said conv nection including a condenser and an in-phase combination of electromagnetic and electrostatic coupling to said tunable circuit.

2. The combination of an amplifier having input and output circuits, a tunable circuit forming a part of one of said circuits, an electromagnetic coupling linking said tunable circuit with the other one of said circuits, and a second coupling therebetween adapted to 10 transfer ener in base with said electroma P e netic coupling, said second coupling having an energy transfer-frequency characteristic the reverse of that of said electromagnetic coupling.

3. The combination of an amplifier having input and output circuits, a tunable circuit formin a part of one of said circuits, a pair of in'pase couplings linking said tunable circuit with the other one of said circuits, said couplings having reversed energy transferfrequency characteristics.

4; The combination of a three-electrode vacuum tube having inherent capacity between its electrodes, a tunable input circuit, an output circuit including an impedance element producing a non-constant impedance with frequency variation, and means for opposing in kind the resulting non-constant with frequency feed-back through said tube capacity comprising a circuit connected between a potential point of said impedance and the cathode of said tube, said circuit includin a series connected condenser outside of sai tunable circuit, a second series connected condenser included within said tunable circuitfand an inductance coil coupled to an inductive coil in said tunable circuit with a polarity to transfer energy in phase with that transferred electrostatically by said second condenser.

5. The combination of a three-electrode vacuum tube having inherent capacity between its electrodes, an input circuit includ-' ing a circuit tunable over a wide range of frequencies, means for suppl ing currents of different frequencies to sai tunable circuit for selection thereby, an output circuit including an associated system roducing a non-constant impedance with requency as said tunable circuit is varied, whereby the amplification of said tube is non-constant with fre uency by reason of varying feed-back t rough said inherent tube capacity, and means associated with said inputcircuit for automatically variably modifying with frequenc the efiect of the non-constant character 0 said feed-back whereby the overall amplification of said system s maintained substantially constant with frequency.

6. The combination of a three-electrode vacuum tube, a tunable circuit including a variable condenser connected across the grid and cathode of said tube including a direct connection to said cathode, an output circuit, and a combined electromagnetic and electrostatic couplings, said energy,

' ing static coupling between said out ut circuit and said tunable circuit, said e ectrostatic coupling. including a condenser in said tunable circuit in series with said variable condenser and common to at least a portion of sa d output circuit, one terminal of said couphng condenser bein connected directly to the cathode of said tu e.

7. The combination of a three-electrode vacuum tube a tunable circuit including. a variable condenser connected across the grid and cathode of said tube including avdirect connection to said cathode, a circuit electromagnetically and electrostatically coupled to said tunable circuit, said electrostatic couphng comprising a condenser in said tunable circuit in series with said variable condenser and common to both circuits, one terminal of said coupling condenser being connected directly to the cathode of said tube.

8. The combination of a plurality of threeelectrode vacuum tubes connected in cascade relation, a circuit at substantially ground potential linking the cathodes of said tubes, tunable circuits each including a mechanically operated tunin condenser connected to the grids of said tu es and directly to said grounded cathode circuit, and circuits'coupled to each of said tunable circuits through a combination of electromagnetic and electroelectrostatic couplings each comprising a condenser in each of said tunable circuits in series with said tuning condensers and common to both circuits, one terminal of each of said coupling condensers being connected directly to said grounded cathode circuit, whereby the movable elements of all of said tuning condensers are maintained at ground potential.

9. In combination, a source of signal an oscillation generator comprising an electron discharge tube having a tunable input circuit coupled to said source and an output circuit, an impedance element in said output circuit, and a pair of in-pliase couplings between the output and input circuits, said couplings having reversed energy transfer-frequency characteristics.

10. Anoscillation generator adapted to produce high frequency oscillations of substantially constant magnitude over a desired frequency range comprlsing a space discharge tube having a tunable input circuit and an output circuit, an impedance in the output circuit, a path from a potential point created by the impedance, in-pha'se combination of electromagnetic and electrostatic coupling to the input circuit.

11. A regenerative am lifier circuit includa multi-electrode to e provided with a tunable input circuit and an output circuit, a load in the output circuit, and a feed back path between the outputcircuit and the input circuit, said path including a pair of mutual impedances of the same sign, but

and said path including an 7 6 v eague o to frequency characteristics, designed tr? a predetermined amplification value throuma ranfifieof 12. Aeta amp rclrcmtmcludmg I I a multi-electrodetube provided with a tun able input circuit, and an outfut circuit, a loadintheoutputcircuit,an afeedback pcth between the on ut circuit and the input circui to coun the inherent feed back o the the tube electrodes, said path including a air of mutuaLimpedancee of the same :1 ut opposite frequency characteristica eslgned to maintain a predetermined amplification value throughout a range of u frequencies.

In witnem whereof, I hereunto subscribe my name this 16th da of Au 1928.

CS NE Y. WHITE. 

